Each component in the design of a laser system is important for the proper functionality of a system as a whole. In particular, the design of an axial flow CO2 laser must contain a gas circulation blower to ensure the performance of the device. The systems' blower has to circulate gases at high velocities through the laser's active plasma region to maintain efficient operation and provide stable laser output power.
There are a variety of gas circulation blowers, or compressors, available for use with the CO2 laser system. Each design has advantages and disadvantages for the specific use and performance of the overall system. Current gas blowers include the regenerative (side-channel), radial (multi-stage), and centrifugal. In addition, there are three types of centrifugal blowers, dependent on the bearing design. The bearing designs include oil mist lubricated radial ball bearings, active magnetic bearings, and gas foil bearings. The regenerative, radial, and oil mist centrifugal blowers all contain contact-type bearings, whereas the active magnet centrifugal blower is a non-contact type bearing. The foil bearing centrifugal blower is a contact-type bearing only at low rotational speeds. However, at operational speeds it acts as a non-contact type bearing.
The regenerative compressor utilizes hybrid ceramic ball bearings with a grease lubricant, reaching peak rotational speeds of about 18,000 rotations per minute (rpm). This compressor requires little maintenance. In addition, any maintenance required, such as bearing replacement, can be done in the field. However, a regenerative compressor is quite inefficient, achieving only 35% pump efficiency. Consequently, the compressor releases up to 65% of its output as waste heat, which is released into the laser system. As a result, this system requires constant cooling to remove the excess heat.
The radial compressor, or gas blower, is the most utilized compressor because of its high laser power output. A single blower can produce a laser power of up to 5,000 Watts (W) and 35,000 rpm. Similar to the regenerative systems, the radial compressor utilizes ceramic ball bearings and a grease lubricant. As with the regenerative compressor, efficiency is approximately 35%. Unlike the regenerative system, however, the radial system is difficult to maintain. Continuing maintenance, which cannot be performed in the field, depends on numerous factors such as supercritical blower operation, below peak efficiency operation (for the size of the system's impeller), and multistage arrangement configuration (for the needed pressure differentials).
A centrifugal blower can utilize any of the aforementioned bearing assemblies and can reach much higher rotational speeds than regenerative or radial blowers, which provides higher pumping efficiencies. For example, pump speeds are approximately 60,000 rpm for a foil blower (although 150,000 rpm has been achieved). Typical rpms for oil mist blowers are approximately 70,000 rpm for an active magnetic blower. However, the principal disadvantage with such a system is that it cannot operate at peak efficiency for the impeller, because the bearings are limited by both speed and load capacity. Also, bearings must have a diameter small enough to limit the rolling surface speed below the damage threshold while supporting the rotational assembly with a high enough stiffness. As a result, an oil mist blower operates at both a relatively lower horsepower (“HP”) and a lower pressure differential than a regenerative pump. These deficiencies are only partially offset by the use of gas bearings.
An active magnet centrifugal blower can operate at peak efficiencies. However, this blower still has several disadvantages. For instance, the magnetic blower is very expensive and contains very complex bearing control units. Further, an active magnetic bearing needs a redundant bearing system in the event of power failure, which results in a loss of magnetizing power.
The original technology for a foil bearing design was developed over 20 years ago. The design was primarily used by NASA and Naval aircrafts, and has been used in air cycle pumps for aircrafts, turbochargers, cryogenic pumps, helium pumps, high speed motors, textile spindles, and more. The basic design is hydrodynamic. A load carrying gas film is created between the shaft and foil as a result of shaft rotation and gas viscosity. This allows for both radial and axial support during shaft rotation, which allows for higher rotational speeds. The higher rotational speed provides more power to pumps at improved efficiencies. Under these conditions a single pump can power a laser up to 8,000 W.
The foil bearing consists of a thin smooth inner surface layer and a bump foil primary, outer surface. The bump design allows for sufficient damping for thermal growth, centrifugal growth, and misalignment of the shaft during high-speed operation.
These conditions, however, do not allow complete freedom of design. Every component of the system must still be assessed to determine if the bump design sufficiently handles the damping at higher speeds. This determination requires an analysis of the rotor dynamics and the thermal characteristics of the blower. However, a majority of the current blowers are not designed to properly handle a foil bearing, and cannot reach the higher rotational speeds necessary for optimum pumping efficiency. Due to these design limitations, the previous blower constraints must be removed and a different blower design must be utilized to maintain the pressure differentials and speeds made available by the foil bearing design.
In addition, efficiency and power consumption depend greatly on the blower functionality within the system. If the system is not properly cooled and/or heated, then it will not function at maximum efficiency. If the blower is more efficient, overall waste heat and power consumption drops dramatically. Therefore, the blower must be designed to maximize efficiency while also functioning within the prescribed requirements of the overall system.
As previously discussed, bearing design has a significant affect on the maintenance of the blower. If the bearings wear easily, they must be replaced more often. Accordingly, it is desirable to design a system wherein the blower and bearings are easily serviceable in their respective environment. Further, such a system should have extended maintenance intervals, which can help reduce costs.
Because current laser systems are expensive, inefficient, and often require repair, there is a clear need in the art for a laser system which is inexpensive, requires little or no maintenance, and is more efficient. The current invention overcomes these and other deficiencies by providing a centrifugal blower with foil bearings. The current invention, therefore, provides a laser system which is cheaper, requires less maintenance, and is more efficient while maintaining requisite output levels.